The glossopharyngeal nerve plays a significant role in oral sensation and function. It mediates the sense of taste from the posterior tongue, and temperature, touch and pain from the pharynx, palate and posterior tongue. Stimulation of these areas initiates reflex activities such as swallowing, gagging , vomiting and coughing. Sensory information from the posterior tongue and pharynx is transmitted to the nucleus of the solitary tract in the brainstem by the glossopharyngeal nerve. Although whole nerve recordings have been made from the glossopharyngeal nerve, it is necessary to examine single fibers to separate the different modalities carried by this nerve. There have been no systematic recordings of neural activity inthe brainstem in response to stimulation of the posterior tongue by each sensory modality. Consequently, it is proposed to record, electrophysiologically, responses of single glossopharyngeal nerve fibers during chemical, thermal and mechanical stimulation of the posterior tongue in lambs. Areas of sensitivity to these stimuli will be located and mapped. The projection area of the posterior tongue in the nucleus of the solitary tract will be determined by electrical stimulation of the peripheral nerve while recording in the brainstem. Subsequently, recordings will be made in the nucleus of the solitary tract while stimulating the posterior tongue with chemical, thermal and mechanical stimuli. The neural activity in both the glossopharyngeal nerve and its brainstem projection needs further systematic study to permit elucidattation of the processes by which sensory input from this reflexogenic area is interpretted by the brain. The proposed research will provide a model of the neural responses from the posterior tongue, and will assist in understanding the role of sensory stimulation in craniofacial function.